The 18-month-old girl is in critical condition at the Alberta Children's Hospital in Calgary. (CBC)

An 18-month-old girl is in critical condition at the Alberta Children's Hospital in Calgary with head injuries police say she sustained at a private home daycare in Medicine Hat.

Police were called to the Medicine Hat Regional Hospital on Monday after the child was taken there with life-threatening injuries. She was then airlifted to the Calgary hospital.

A 23-year-old woman, who was the daycare provider, has been charged with one count of aggravated assault and one count of failing to provide the necessities of life, Medicine Hat police Staff Sgt. Brent Secondiak said Tuesday.

The woman was taking care of only the one child at the time in the provincially approved day home, and no other children are at risk, he said.

The accused has been released from custody and is scheduled to appear in court again on Sept. 7.

The Medicine Hat police major crimes section continues to investigate what happened.

2,800 day homes in Alberta

The province approves day homes, which provide care for up to six children in private residences. The day homes are monitored and contracted by agencies.

Alberta's 2,800 day homes are not licensed but must follow 12 standards that include criminal record checks, proper training, and certain hours of service.

"A situation like this is extremely unusual. It's very rare," Yvonne Fritz, minister of children and youth services, said Tuesday. She said she could not comment specifically on the Medicine Hat day home, but confirmed her department is investigating whether it met provincial standards.

"It would be inappropriate to comment about any specifics of the day home as the police have not released the name of the accused," she said.

With files from The Canadian Press